610 Mr. W. A. Borodowsky on Absorption of 



Experiments I. to III. give the effect of dilution o£ an 

 electrolytic solution, and IV. of a non-electrolytic solution. 

 It will be seen that there is practically no change in the 

 activity after mixing. With a viscous solution like sugar, a 

 small amount of liquid sticks to the mica and is removed 

 with it. This is spread over a large area, and so the effective 

 mass in producing absorption is a little less. This accounts 

 for the slight diminution in activity observed in case IV. 



Experiment V. gives the effect when one substance is 

 precipitated from the solution on mixing, and VI. the effect 

 when two substances are precipitated. In the latter case 

 equivalent amounts of solution were taken, so that after 

 mixture the silver and barium were both completely preci- 

 pitated. In all these experiments the variation of activity 

 lies within the limits of error of observation. 



If the cells are not full to the top and covered with mica, 

 the ft ray activity before and after mixing of solutions is not 

 the same, e.g. for a mixture of H 2 S0 4 and H 2 a 12 per cent, 

 change in the activity was observed, while for a mixture of 

 sugar and H 2 the change was about 21 per cent. This is 

 due to the fact that the surface tension alters on mixing; 

 the meniscus becomes flatter and the effective thickness of 

 matter in the path of the ft particles becomes greater. 



The results of the above experiments show conclusively 

 that the absorption of ft rays is independent of the physical 

 or chemical state of the solution. 



Method of comparing Absorption in terms of A luminium. 



Since the ft particles from radium bromide in a state of 

 radioactive equilibrium are not absorbed according to an 

 exponential law, it is advisable to express the results of 

 absorption by different liquids in terms of the absorption 

 by a definite metal, for example, by aluminium. 



In order to compare the absorption of the ft rays by liquids 

 with that by aluminium, thin sheets of aluminium ('078 mm. 

 thick) were put between the strips of the glass wedge and 

 the variation of activity with increase of thickness was 

 plotted. The initial activity, taken as 100 per cent., repre- 

 sents, as in the case of solutions, the effect of the ft and 

 7 rays passing through the empty wedge. The decrease of 

 the activity with increase of thickness of the layer of the 

 solution was plotted on a iarge scale on the same paper on 

 which a similar curve for aluminium was drawn. 



Examples of typical curves obtained in this way are given 

 in figs. 3 and 4. 



